Layers of the atmosphere | NIWA Layers of the atmosphere Post-Doctoral Fellowships Layers of the atmosphere The atmosphere is comprised of layers based on temperature. These layers are the troposphere, stratosphere, mesosphere and thermosphere. A further region at about 500 km above the Earth's surface is called the exosphere. The different layers of the atmosphere The atmosphere can be divided into layers based on its temperature, as shown in the figure below. These layers are the troposphere, the stratosphere, the mesosphere and the thermosphere. A further region, beginning about 500 km above the Earth's surface, is called the exosphere. The red line on the figure below shows how temperature varies with height (the temperature scale is given along the bottom of the diagram). The scale on the right shows the pressure. For example, at a height of 50 km, the pressure is only about one thousandth of the pressure at the ground. The Troposphere This is the lowest part of the atmosphere - the part we live in. It contains most of our weather - clouds, rain, snow.

In this part of the atmosphere the temperature gets colder as the distance above the earth increases, by about 6.5°C per kilometre. The actual change of temperature with height varies from day to day, depending on the weather. The troposphere contains about 75% of all of the air in the atmosphere, and almost all of the water vapour (which forms clouds and rain). The decrease in temperature with height is a result of the decreasing pressure. If a parcel of air moves upwards it expands (because of the lower pressure). When air expands it cools. So air higher up is cooler than air lower down. The lowest part of the troposphere is called the boundary layer. This is where the air motion is determined by the properties of the Earth's surface. Turbulence is generated as the wind blows over the Earth's surface, and by thermals rising from the land as it is heated by the sun. This turbulence redistributes heat and moisture within the boundary layer, as well as pollutants and other constituents of the atmosphere. The top of the troposphere is called the tropopause. This is lowest at the poles, where it is about 7 - 10 km above the Earth's surface.

It is highest (about 17 - 18 km) near the equator. The Stratosphere This extends upwards from the tropopause to about 50 km. It contains much of the ozone in the atmosphere. The increase in temperature with height occurs because of absorption of ultraviolet (UV) radiation from the sun by this ozone. Temperatures in the stratosphere are highest over the summer pole, and lowest over the winter pole. By absorbing dangerous UV radiation, the ozone in the stratosphere protects us from skin cancer and other health damage. However chemicals (called CFCs or freons, and halons) which were once used in refrigerators, spray cans and fire extinguishers have reduced the amount of ozone in the stratosphere, particularly at polar latitudes, leading to the so-called "Antarctic ozone hole". Now humans have stopped making most of the harmful CFCs we expect the ozone hole will eventually recover over the 21st century, but this is a slow process. The Mesosphere The region above the stratosphere is called the mesosphere. Here the temperature again decreases with height, reaching a minimum of about -90°C at the "mesopause".

The Thermosphere and Ionosphere The thermosphere lies above the mesopause, and is a region in which temperatures again increase with height. This temperature increase is caused by the absorption of energetic ultraviolet and X-Ray radiation from the sun. The region of the atmosphere above about 80 km is also caused the "ionosphere", since the energetic solar radiation knocks electrons off molecules and atoms, turning them into "ions" with a positive charge. The temperature of the thermosphere varies between night and day and between the seasons, as do the numbers of ions and electrons which are present. The ionosphere reflects and absorbs radio waves, allowing us to receive shortwave radio broadcasts in New Zealand from other parts of the world. The Exosphere The region above about 500 km is called the exosphere. It contains mainly oxygen and hydrogen atoms, but there are so few of them that they rarely collide - they follow "ballistic" trajectories under the influence of gravity, and some of them escape right out into space. The Magnetosphere The earth behaves like a huge magnet.

It traps electrons (negative charge) and protons (positive), concentrating them in two bands about 3,000 and 16,000 km above the globe - the Van Allen "radiation" belts. This outer region surrounding the earth, where charged particles spiral along the magnetic field lines, is called the magnetosphere. Further information Layers of Earth's Atmosphere - Windows to the Universe Layers of Earth's Atmosphere The Earth's Atmosphere The atmosphere surrounds Earth and protects us by blocking out dangerous rays from the sun. The atmosphere is a mixture of gases that becomes thinner until it gradually reaches space. It is composed of Nitrogen (78%), Oxygen (21%), and other gases (1%). Oxygen is essential to life because it allows us to breathe. Some of the oxygen has changed over time to ozone. The the ozone layer filters out the sun's harmful rays. Recently, there have been many studies on how humans have caused a hole in the ozone layer. Humans are also affecting Earth's atmosphere through the greenhouse effect. Due to increases in gases, like carbon dioxide, that trap heat being radiated from the Earth, scientists believe that the atmosphere is having trouble staying in balance creating the greenhouse effect .

The atmosphere is divided into five layers depending on how temperature changes with height. Most of the weather occurs in the first layer. Layers of the Earth's Atmosphere The atmosphere is divided into five layers. It is thickest near the surface and thins out with height until it eventually merges with space. The troposphere is the first layer above the surface and contains half of the Earth's atmosphere. Weather occurs in this layer. Many jet aircrafts fly in the stratosphere because it is very stable. Also, the ozone layer absorbs harmful rays from the Sun. Meteors or rock fragments burn up in the mesosphere. The thermosphere is a layer with auroras. It is also where the space shuttle orbits. The atmosphere merges into space in the extremely thin exosphere. This is the upper limit of our atmosphere. The Average Temperature Profile of Earth's Atmosphere The Troposphere The troposphere is the lowest layer of the Earth's atmosphere. The air is very well mixed and the temperature decreases with altitude. Air in the troposphere is heated from the ground up. The surface of the Earth absorbs energy and heats up faster than the air does. The heat is spread through the troposphere because the air is slightly unstable.

Weather occurs in the Earth's troposphere. The Stratosphere In the Earth's stratosphere, the temperature increases with altitude. On Earth, ozone causes the increasing temperature in the stratosphere. Ozone is concentrated around an altitude of 25 kilometers. The ozone molecules absorb dangerous kinds of sunlight, which heats the air around them. The stratosphere is located above the top of the the troposphere. Ozone - An Overview The Ozone Hole. Pollution. Skin Cancer. Why does the topic of ozone make the news so much? How important is the ozone in our atmosphere? Why are scientists so concerned about its increase near the surface of the Earth and its disappearance higher up in the atmosphere? First things first - what is ozone? Ozone is made of three oxygen atoms (O3). The oxygen in our atmosphere that we breathe is made up of two oxygen atoms (O2). When enough ozone molecules are present, it forms a pale blue gas. Ozone has the same chemical structure whether it is found in the stratosphere or the troposphere. Where we find ozone in the atmosphere determines whether we consider it to be "good" or "bad"!

In the troposphere, the ground-level or "bad" ozone is an air pollutant that damages human health, vegetation, and many common materials. It is a key ingredient of urban smog. In the stratosphere, we find the "good" ozone that protects life on Earth from the harmful effects of the Sun's ultraviolet rays. We have good reason to be concerned about the thinning of the ozone layer in the stratosphere. We also have good reason to be concerned about the buildup of ozone in the troposphere. Although simplistic, the saying "Good up high and bad near by," sums up ozone in the atmosphere. Ozone in the Stratosphere About 90% of the ozone in the Earth's atmosphere is found in the region called the stratosphere. This is the atmospheric layer between 16 and 48 kilometers (10 and 30 miles) above the Earth's surface. Ozone forms a kind of layer in the stratosphere, where it is more concentrated than anywhere else. Ozone and oxygen molecules in the stratosphere absorb ultraviolet light from the Sun, providing a shield that prevents this radiation from passing to the Earth's surface.

While both oxygen and ozone together absorb 95 to 99.9% of the Sun's ultraviolet radiation, only ozone effectively absorbs the most energetic ultraviolet light, known as UV-C and UV-B. This ultraviolet light can cause biological damage like skin cancer, tissue damage to eyes and plant tissue damage. The protective role of the ozone layer in the upper atmosphere is so vital that scientists believe life on land probably would not have evolved - and could not exist today - without it. The ozone layer would be quite good at its job of protecting Earth from too much ultraviolet radiation - that is, it would if humans did not contribute to the process. It's now known that ozone is destroyed in the stratosphere and that some human-released chemicals such as CFCï¿½s are speeding up the breakdown of ozone, so that there are "holes" now in our protective shield. While the stratospheric ozone issue is a serious one, in many ways it can be thought of as an environmental success story. Scientists detected the developing problem, and collected the evidence that convinced governments around the world to take action. Although the elimination of ozone-depleting chemicals from the atmosphere will take decades yet, we have made a strong and positive beginning.

For the first time in our species' history, we have tackled a global environmental issue on a global scale. The Mesosphere In the Earth's mesosphere, the air is relatively mixed together and the temperature decreases with altitude. The atmosphere reaches its coldest temperature of around -90ï¿½C in the mesosphere. This is also the layer in which a lot of meteors burn up while entering the Earth's atmosphere. The mesosphere is on top of the stratosphere The upper parts of the atmosphere, such as the mesosphere, can sometimes be seen by looking at the very edge of a planet. The Thermosphere The thermosphere is the fourth layer of the Earth's atmosphere and is located above the mesosphere. The air is really thin in the thermosphere. A small change in energy can cause a large change in temperature. That's why the temperature is very sensitive to solar activity. When the sun is active, the thermosphere can heat up to 1,500ï¿½ C or higher! The Earth's thermosphere also includes the region of the atmosphere called the ionosphere. The ionosphere is a region of the atmosphere that is filled with charged particles.

The high temperatures in the thermosphere can cause molecules to ionize. This is why an ionosphere and thermosphere can overlap. The Ionosphere Scientists call the ionosphere an extension of the thermosphere. So technically, the ionosphere is not another atmospheric layer. The ionosphere represents less than 0.1% of the total mass of the Earth's atmosphere. Even though it is such a small part, it is extremely important! The upper atmosphere is ionized by solar radiation. That means the Sun's energy is so strong at this level, that it breaks apart molecules. So there ends up being electrons floating around and molecules which have lost or gained electrons. When the Sun is active, more and more ionization happens! Different regions of the ionosphere make long distance radio communication possible by reflecting the radio waves back to Earth. It is also home to auroras. Temperatures in the ionosphere just keep getting hotter as you go up! Regions of the Ionosphere The ionosphere is broken down into the D, E and F regions. The breakdown is based on what wavelength of solar radiation is absorbed in that region most frequently. The D region is the lowest in altitude, though it absorbs the most energetic radiation, hard x-rays.

The D region doesn't have a definite starting and stopping point, but includes the ionization that occurs below about 90km. The E region peaks at about 105km. It absorbs soft x-rays. The F region starts around 105km and has a maximum around 600km. It is the highest of all of the regions. Extreme ultra-violet radiation (EUV) is absorbed there. On a more practical note, the D and E regions reflect AM radio waves back to Earth. Radio waves with shorter lengths are reflected by the F region. Visible light, television and FM wavelengths are all too short to be reflected by the ionosphere. So your t.v. stations are made possible by satellite transmissions. This image shows how the ionosphere is divided even further into layers: D, E, and F layers. The Sun's Effect on the Ionosphere Invisible layers of ions and electrons are found in the Earth's atmosphere. We call this region of atmosphere the ionosphere. The main source of these layers is the Sun's ultraviolet light which ionizes atoms and molecules in the Earth's upper atmosphere. During this process, electrons are knocked free from molecules or particles in the atmosphere.

Flares and other big events on the Sun produce increased ultraviolet, x-ray and gamma-ray photons that arrive at the Earth just 8 minutes later (other particles from the Sun may arrive days later) and dramatically increase the ionization that happens in the atmosphere. So, the more active the Sun, the thicker the ionosphere! This image shows how different types of solar radiation (x-rays to infrared radiation) penetrate into the Earth's atmosphere. It is this solar radiation that ionizes the upper atmosphere, creating the ionosphere. The Exosphere Very high up, the Earth's atmosphere becomes very thin. The region where atoms and molecules escape into space is referred to as the exosphere. The exosphere is on top of the thermosphere. Last modified September 1, 2010 by Randy Russell . Shop Windows to the Universe Science Store! The Fall 2009 issue of The Earth Scientist , which includes articles on student research into building design for earthquakes and a classroom lab on the composition of the Earthï¿½s ancient atmosphere, is available in our online store .

Windows to the Universe Community News Layers of Earth's Atmosphere | UCAR Center for Science Education Layers of Earth's Atmosphere Layers of the atmosphere: troposphere, stratosphere, mesosphere and thermosphere. Credit: Randy Russell, UCAR Earth's atmosphere has a series of layers, each with its own specific traits. Moving upward from ground level, these layers are named the troposphere, stratosphere, mesosphere, thermosphere and exosphere. The exosphere gradually fades away into the realm of interplanetary space. Troposphere The troposphere is the lowest layer of our atmosphere. Starting at ground level, it extends upward to about 10 km (6.2 miles or about 33,000 feet) above sea level. We humans live in the troposphere, and nearly all weather occurs in this lowest layer. Most clouds appear here, mainly because 99% of the water vapor in the atmosphere is found in the troposphere. Air pressure drops, and temperatures get colder, as you climb higher in the troposphere. Stratosphere The next layer up is called the stratosphere .

The stratosphere extends from the top of the troposphere to about 50 km (31 miles) above the ground. The infamous ozone layer is found within the stratosphere. Ozone molecules in this layer absorb high-energy ultraviolet (UV) light from the Sun, converting the UV energy into heat. Unlike the troposphere, the stratosphere actually gets warmer the higher you go! That trend of rising temperatures with altitude means that air in the stratosphere lacks the turbulence and updrafts of the troposphere beneath. Commercial passenger jets fly in the lower stratosphere, partly because this less-turbulent layer provides a smoother ride. The jet stream flows near the border between the troposphere and the stratosphere. Mesosphere Above the stratosphere is the mesosphere . It extends upward to a height of about 85 km (53 miles) above our planet. Most meteors burn up in the mesosphere. Unlike the stratosphere, temperatures once again grow colder as you rise up through the mesosphere. The coldest temperatures in Earth's atmosphere, about -90° C (-130° F), are found near the top of this layer.

The air in the mesosphere is far too thin to breathe; air pressure at the bottom of the layer is well below 1% of the pressure at sea level, and continues dropping as you go higher. Thermosphere The layer of very rare air above the mesosphere is called the thermosphere . High-energy X-rays and UV radiation from the Sun are absorbed in the thermosphere, raising its temperature to hundreds or at times thousands of degrees. However, the air in this layer is so thin that it would feel freezing cold to us! In many ways, the thermosphere is more like outer space than a part of the atmosphere. Many satellites actually orbit Earth within the thermosphere! Variations in the amount of energy coming from the Sun exert a powerful influence on both the height of the top of this layer and the temperature within it. Because of this, the top of the thermosphere can be found anywhere between 500 and 1,000 km (311 to 621 miles) above the ground.

Temperatures in the upper thermosphere can range from about 500° C (932° F) to 2,000° C (3,632° F) or higher. The aurora, the Northern Lights and Southern Lights, occur in the thermosphere. Exosphere Although some experts consider the thermosphere to be the uppermost layer of our atmosphere, others consider the exosphere to be the actual "final frontier" of Earth's gaseous envelope. As you might imagine, the "air" in the exosphere is very, very, very thin, making this layer even more space-like than the thermosphere. In fact, air in the exosphere is constantly - though very gradually - "leaking" out of Earth's atmosphere into outer space. There is no clear-cut upper boundary where the exosphere finally fades away into space. Different definitions place the top of the exosphere somewhere between 100,000 km (62,000 miles) and 190,000 km (120,000 miles) above the surface of Earth. The latter value is about halfway to the Moon!

NWS JetStream - Layers of the Atmosphere NWS JetStream myForecast Layers of the Atmosphere The envelope of gas surrounding the Earth changes from the ground up. Five distinct layers have been identified using... thermal characteristics (temperature changes), movement, and density. Each of the layers are bounded by "pauses" where the greatest changes in thermal characteristics, chemical composition, movement, and density occur. The five basic layers of the atmosphere Exosphere This is the outermost layer of the atmosphere. It extends from the top of the thermosphere to 6,200 miles (10,000 km ) above the earth. In this layer, atoms and molecules escape into space and satellites orbit the earth. At the bottom of the exosphere is the thermopause located around 375 miles (600 km) above the earth. Thermosphere Between about 53 miles (85 km) and 375 miles (600 km) lies the thermosphere. This layer is known as the upper atmosphere. While still extremely thin, the gases of the thermosphere become increasingly more dense as one descends toward the earth.

As such, incoming high energy ultraviolet and x-ray radiation from the sun begins to be absorbed by the molecules in this layer and causes a large temperature increase. Because of this absorption, the temperature increases with height. From as low as -184 °F (-120 °C ) at the bottom of this layer, temperatures can reach as high as 3,600°F (2,000°C) near the top. However, despite the high temperature, this layer of the atmosphere would still feel very cold to our skin due to the very thin atmosphere. The high temperature indicates the amount of the energy absorbed by the molecules but with so few in this layer, the total number of molecules is not enough to heat our skin. Take it to the MAX! The Ionosphere Mesosphere This layer extends from around 31 miles (50 km) above the Earth's surface to 53 miles (85 km). The gases, including the oxygen molecules, continue to become more dense as one descends. As such, temperatures increase as one descends rising to about 5°F (-15°C) near the bottom of this layer.

The gases in the mesosphere are now thick enough to slow down meteors hurtling into the atmosphere, where they burn up, leaving fiery trails in the night sky. Both the stratosphere (next layer down) and the mesosphere are considered the middle atmosphere. The transition boundary which separates the mesosphere from the stratosphere is called the stratopause. Stratosphere The Stratosphere extends around 31 miles (50 km) down to anywhere from 4 to 12 miles (6 to 20 km) above the Earth's surface. This layer holds 19 percent of the atmosphere's gases but very little water vapor. In this region the temperature increases with height. Heat is produced in the process of the formation of Ozone and this heat is responsible for temperature increases from an average -60°F (-51°C) at tropopause to a maximum of about 5°F (-15°C) at the top of the stratosphere. This increase in temperature with height means warmer air is located above cooler air. This prevents "convection" as there is no upward vertical movement of the gases.

As such the location of the bottom of this layer is readily seen by the 'anvil-shaped' tops of cumulonimbus clouds. Troposphere Known as the lower atmosphere almost all weather occurs in this region. The troposphere begins at the Earth's surface and extends from 4 to 12 miles (6 to 20 km) high. The height of the troposphere varies from the equator to the poles. At the equator it is around 11-12 miles (18-20 km) high, at 50 °N and 50 °S , 5½ miles and at the poles just under four miles high. As the density of the gases in this layer decrease with height, the air becomes thinner. Therefore, the temperature in the troposphere also decreases with height in response. As one climbs higher, the temperature drops from an average around 62°F (17°C) to -60°F (-51°C) at the tropopause. Average temperature profile for the lower layers of the atmosphere atmosphere - National Geographic Society atmosphere Our atmosphere—the thin blue line.

Photograph courtesy NASA Atmospheric Orbit Although the International Space Station orbits in the thermosphere, most satellites orbit the Earth outside its atmosphere. GPS satellites, for instance, are in orbit more than 20,000 kilometers (12,400 miles) above the Earth. Magnetosphere Earths magnetosphere is not considered part of the atmosphere. The magnetosphere, formed by the Earths magnetic fields, protects the atmosphere by preventing it from being blown away by powerful solar wind. Ingredients for Life Scientists have gathered enough information about other planets in our solar system to know that none can support life as we know it. Life is not possible without a stable atmosphere containing the right chemical ingredients for living organisms: hydrogen, oxygen, nitrogen, and carbon. These ingredients must be balanced—not too thick or too thin. Life also depends on the presence of water. Jupiter, Saturn, Uranus, and Neptune all have atmospheres made mostly of hydrogen and helium. These planets are called gas giants, because they are mostly made of gas and do not have a solid outer crust. Mercury and Mars have some of the right ingredients, but their atmospheres are far too thin to support life.

The atmosphere of Venus is too thick—the planet's surface temperature is more than 460 degrees Celsius (860 degrees Fahrenheit). Jupiter's moon Europa has a thin atmosphere rich with oxygen. It is likely covered by a huge ocean of liquid water. Some astrobiologists think that if life will develop elsewhere in the solar system, it will be near vents at the bottom of Europa's ocean. We live at the bottom of an invisible ocean called the atmosphere , a layer of gases surrounding our planet . Nitrogen and oxygen account for 99 percent of the gases in dry air , with argon , carbon dioxide , helium , neon , and other gases making up minute portions. Water vapor and dust are also part of Earth ’s atmosphere. Other planets and moons have very different atmospheres, and some have no atmospheres at all. The atmosphere is so spread out that we barely notice it, yet its weight is equal to a layer of water more than 10 meters (34 feet) deep covering the entire planet. The bottom 30 kilometers (19 miles) of the atmosphere contains about 98 percent of its mass . The atmosphere—air—is much thinner at high altitudes. There is no atmosphere in space.

Scientists say many of the gases in our atmosphere were ejected into the air by early volcanoes. At that time, there would have been little or no free oxygen surrounding the Earth. Free oxygen consists of oxygen molecules not attached to another element , like carbon (to form carbon dioxide) or hydrogen (to form water). Free oxygen may have been added to the atmosphere by primitive organisms, probably bacteria , during photosynthesis . Photosynthesis is the process a plant or other autotroph uses to make food and oxygen from carbon dioxide and water. Later, more complex forms of plant life added more oxygen to the atmosphere. The oxygen in today’s atmosphere probably took millions of years to accumulate . The atmosphere acts as a gigantic filter , keeping out most ultraviolet radiation while letting in the sun’s warming rays. Ultraviolet radiation is harmful to living things, and is what causes sunburns. Solar heat, on the other hand, is necessary for all life on Earth. Earth’s atmosphere has a layered structure. From the ground toward the sky, the layers are the troposphere , stratosphere , mesosphere , thermosphere , and exosphere . Another layer, called the ionosphere , extends from the mesosphere to the exosphere. Beyond the exosphere is outer space .

The boundaries between atmospheric layers are not clearly defined, and change depending on latitude and season . Troposphere The troposphere is the lowest atmospheric layer. On average, the troposphere extends from the ground to about 10 kilometers (6 miles) high, ranging from about 6 kilometers (4 miles) at the poles to more than 16 kilometers (10 miles) at the Equator . The top of the troposphere is higher in summer than in winter. Almost all weather develops in the troposphere because it contains almost all of the atmosphere’s water vapor. Clouds, from low-lying fog to thunderheads to high- altitude cirrus , form in the troposphere. Air masses, areas of high-pressure and low-pressure systems, are moved by winds in the troposphere. These weather systems lead to daily weather changes as well as seasonal weather patterns and climate systems, such as El Nino . Air in the troposphere thins as altitude increases. There are fewer molecules of oxygen at the top of Mount Everest , Nepal, for example, than there are on a beach in Hawaii. This is why mountaineers often use canisters of oxygen when climbing tall peaks. Thin air is also why helicopters have difficulty maneuvering at high altitudes.

In fact, a helicopter was not able to land on Mount Everest until 2005. As air in the troposphere thins, temperature decreases. This is why mountaintops are usually much colder than the valleys beneath. Scientists used to think temperature continued to drop as altitude increased beyond the troposphere. But data collected with weather balloons and rockets have showed this is not the case. In the lower stratosphere, temperature stays almost constant. As altitude increases in the stratosphere, temperature actually increases. Solar heat penetrates the troposphere easily. This layer also absorbs heat that is reflected back from the ground in a process called the greenhouse effect . The greenhouse effect is necessary for life on Earth. The atmosphere’s most abundant greenhouse gases are carbon dioxide, water vapor, and methane . Fast-moving, high-altitude winds called jet streams swirl around the planet near the upper boundary of the troposphere. Jet streams are extremely important to the airline industry. Aircraft save time and money by flying in jet streams instead of the lower troposphere, where air is thicker. Stratosphere The troposphere tends to change suddenly and violently, but the stratosphere is calm.

The stratosphere extends from the tropopause , the upper boundary of the troposphere, to about 50 kilometers (32 miles) above the Earth’s surface. Strong horizontal winds blow in the stratosphere, but there is little turbulence. This is ideal for planes that can fly in this part of the atmosphere. The stratosphere is very dry and clouds are rare. Those that do form are thin and wispy. They are called nacreous clouds. Sometimes they are called mother-of-pearl clouds because their colors look like those inside a mollusk shell. The stratosphere is crucial to life on Earth because it contains small amounts of ozone , a form of oxygen that prevents harmful UV rays from reaching Earth. The region within the stratosphere where this thin shell of ozone is found is called the ozone layer . The stratosphere’s ozone layer is uneven, and thinner near the poles. The amount of ozone in the Earth’s atmosphere is declining steadily. Scientists have linked use of chemicals such as chlorofluorocarbons (CFCs) to ozone depletion .

Mesosphere The mesosphere extends from the stratopause (the upper boundary of the stratosphere) to about 85 kilometers (53 miles) above the surface of the Earth. Here, temperatures again begin to fall. The mesosphere has the coldest temperatures in the atmosphere, dipping as low as -120 degrees Celsius (-184 degrees Fahrenheit, or 153 kelvin). The mesosphere also has the atmosphere’s highest clouds. In clear weather, you can sometimes see them as silvery wisps immediately after sunset. They are called noctilucent clouds, or night-shining clouds. The mesosphere is so cold that noctilucent clouds are actually frozen water vapor— ice clouds. Shooting stars—the fiery burnout of meteors, dust, and rocks from outer space—are visible in the mesosphere. Most shooting stars are the size of a grain of sand and burn up before entering the stratosphere or troposphere. However, some meteors are the size of pebbles or even boulders. Their outer layers burn as they race through the mesosphere, but they are massive enough to fall through the lower atmosphere and crash to Earth as meteorites.

The mesosphere is the least-understood part of Earth’s atmosphere. It is too high for aircraft or weather balloons to operate, but too low for spacecraft . Sounding rockets have provided meteorologists and astronomers their only significant data on this important part of the atmosphere. Sounding rockets are unmanned research instruments that collect data during sub-orbital flights. Perhaps because the mesosphere is so little understood, it is home to two meteorological mysteries: sprites and elves . Sprites are reddish, vertical electrical discharges that appear high above thunderheads, in the upper stratosphere and mesosphere. Elves are dim, halo-shaped discharges that appear even higher in the mesosphere. Ionosphere The ionosphere extends from the top half of the mesosphere all the way to the exosphere. This atmospheric layer conducts electricity . The ionosphere is named for ions created by energetic particles from sunlight and outer space. Ions are atoms in which the number of electrons does not equal the number of protons, giving the atom a positive (fewer electrons than protons) or negative (more electrons than protons) charge. Ions are created as powerful x-rays and UV rays knock electrons off atoms.

The ionosphere—a layer of free electrons and ions—reflects radio waves. Guglielmo Marconi , the “Father of Wireless,” helped prove this in 1901 when he sent a radio signal from Cornwall, England, to St. John’s, Newfoundland, Canada. Marconi’s experiment demonstrated that radio signals did not travel in a straight line, but bounced off an atmospheric layer—the ionosphere. The ionosphere is broken into distinct layers, called the D, E, F1, and F2 layers. Like all other parts of the atmosphere, these layers vary with season and latitude. Changes in the ionosphere actually happen on a daily basis. The low D layer, which absorbs high-frequency radio waves, and the E layer actually disappear at night, which means radio waves can reach higher into the ionosphere. That’s why AM radio stations can extend their range by hundreds of kilometers every night. The ionosphere also reflects particles from solar wind , the stream of highly charged particles ejected by the sun. These electrical displays create auroras (light displays) called the Northern and Southern Lights . Thermosphere The thermosphere is the thickest layer in the atmosphere.

Only the lightest gases—mostly oxygen, helium, and hydrogen—are found here. The thermosphere extends from the mesopause (the upper boundary of the mesosphere) to 690 kilometers (429 miles) above the surface of the Earth. Here, thinly scattered molecules of gas absorb x-rays and ultraviolet radiation. This absorption process propels the molecules in the thermosphere to great speeds and high temperatures. Temperatures in the thermosphere can rise to 1,500 degrees Celsius (2,732 degrees Fahrenheit, or 1,773 kelvin). Though the temperature is very high, there is not much heat. How is that possible? Heat is created when molecules get excited and transfer energy from one molecule to another. Heat happens in an area of high pressure (think of water boiling in a pot). Since there is very little pressure in the thermosphere, there is little heat transfer. The Hubble Space Telescope and the International Space Station (ISS) orbit the Earth in the thermosphere.

Even though the thermosphere is the second-highest layer of Earth’s atmosphere, satellites that operate here are in “ low-Earth orbit .” Exosphere The fluctuating area between the thermosphere and the exosphere is called the turbopause . The lowest level of the exosphere is called the exobase . At the upper boundary of the exosphere, the ionosphere merges with interplanetary space , or the space between planets. The exosphere expands and contracts as it comes into contact with solar storms. In solar storms particles are flung through space from explosive events on the sun, such as solar flares and coronal mass ejections (CMEs). Solar storms can squeeze the exosphere to just 1,000 kilometers (620 miles) above the Earth. When the sun is calm, the exosphere can extend 10,000 kilometers (6,214 miles). Hydrogen, the lightest element in the universe , dominates the thin atmosphere of the exosphere. Only trace amounts of helium, carbon dioxide, oxygen, and other gases are present. Many weather satellites orbit Earth in the exosphere.

The lower part of the exosphere includes low-Earth orbit, while medium-Earth orbit is higher in the atmosphere. The upper boundary of the exosphere is visible in satellite images of Earth. Called the geocorona , it is the fuzzy blue illumination that circles the Earth. Extraterrestrial Atmospheres All the planets in our solar system have atmospheres. Most of these atmospheres are radically different from Earth’s, although they contain many of the same elements. The solar system has two major types of planets: terrestrial planets (Mercury, Venus, Earth, and Mars) and gas giants (Jupiter, Saturn, Uranus, and Neptune). The atmospheres of the terrestrial planets are somewhat similar to Earth’s. Mercury’s atmosphere contains only a thin exosphere dominated by hydrogen, helium, and oxygen. Venus’ atmosphere is much thicker than Earth’s, preventing a clear view of the planet. Its atmosphere is dominated by carbon dioxide, and features swirling clouds of sulfuric acid . The atmosphere on Mars is also dominated by carbon dioxide, although unlike Venus, it is quite thin. Gas giants are composed of gases. Their atmospheres are almost entirely hydrogen and helium.

The presence of methane in the atmospheres of Uranus and Neptune give the planets their bright blue color. In the lower atmospheres of Jupiter and Saturn, clouds of water, ammonia , and hydrogen sulfide form clear bands. Fast winds separate light-colored bands, called zones, from dark-colored bands, called belts. Other weather phenomena , such as cyclones and lightning , create patterns in the zones and belts. Jupiter’s Great Red Spot is a centuries-old cyclone that is the largest storm in the solar system. The moons of some planets have their own atmospheres. Saturn’s largest moon , Titan , has a thick atmosphere made mostly of nitrogen and methane. The way sunlight breaks up methane in Titan’s ionosphere helps give the moon an orange color. Most celestial bodies, including all the asteroids in the asteroid belt and our own moon, do not have atmospheres. The lack of an atmosphere on the Moon means it does not experience weather. With no wind or water to erode them, many craters on the Moon have been there for hundreds and even thousands of years. The way a celestial body ’s atmosphere is structured and what it’s made of allow astrobiologists to speculate what kind of life the planet or moon may be able to support.

Atmospheres, then, are important markers in space exploration. A planet or moon’s atmosphere must contain specific chemicals to support life as we know it. These chemicals include hydrogen, oxygen, nitrogen, and carbon . Although Venus, Mars, and Titan have similar atmospheric gases, there is nowhere in the solar system besides Earth with an atmosphere able to support life. Venus’ atmosphere is far too thick, Mars’ far too thin, and Titan’s far too cold. Term vehicle able to travel and operate above the ground. airline system or business that provides air transportation. air mass a gas (NH3) important to food production. AM radio Noun (amplitude modification) method of radio communication using amplitude modification, or varying the strength of the radio signal. argon chemical element (gas) with the symbol Ar. asteroid Noun irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter. asteroid belt area of the solar system between the orbits of Mars and Jupiter filled with asteroids. astrobiologist person who studies the possibility of life in outer space.

astronomer person who studies space and the universe beyond Earth's atmosphere. atmosphere the basic unit of an element, composed of three major parts: electrons, protons, and neutrons. aurora Noun brightly colored bands of light, visible around Earth's geomagnetic poles, caused by solar wind interacting with particles in Earth's magnetic field. autotroph Noun organism that can produce its own food and nutrients from chemicals in the atmosphere, usually through photosynthesis or chemosynthesis. (singular: bacterium) single-celled organisms found in every ecosystem on Earth. beach dark-colored band of clouds on Jupiter or Saturn. boulder container, usually shaped like a long tube. carbon chemical element with the symbol C, which forms the basis of all known life. carbon dioxide Noun greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels. celestial body natural object in space, such as a planet or star. Also called an astronomical object. chlorofluorocarbon (CFC) Noun chemical compound mostly used in refrigerants and flame-retardants. Some CFCs have destructive effects on the ozone layer. cirrus to shrink or get smaller.

coronal mass ejection huge burst of solar wind and other charged particles. crater cyclone Noun weather system that rotates around a center of low pressure and includes thunderstorms and rain. Usually, hurricanes refer to cyclones that form over the Atlantic Ocean. data (singular: datum) information collected during a scientific study. dominate standard measurement of gases that make up air at sea level, excluding water vapor. dust Earth Noun our planet, the third from the Sun. The Earth is the only place in the known universe that supports life. to get rid of or throw out. electricity set of physical phenomena associated with the presence and flow of electric charge. electron chemical that cannot be separated into simpler substances. El Nino Noun elves Plural Noun (Emissions of Light and Very low-frequency perturbations from Electromagnetic pulse Sources) halo-shaped electrical discharge in the upper atmosphere, usually appearing above sprites. Equator lowest level of the exosphere layer of Earth's atmosphere. exosphere Noun outermost layer of Earth's atmosphere, beginning at an altitude of about 550 kilometers (341 miles) above the Earth's surface.

expand filter Verb to remove particles from a substance by passing the substance through a screen or other material that catches larger particles and lets the rest of the substance pass through. fluctuate to constantly change back and forth. fog electron that has been temporarily knocked off an atom. free oxygen oxygen molecules that are not attached to other atoms or molecules. gas Noun state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion. gas giant Noun one of the four enormous outermost planets in the solar system (Jupiter, Saturn, Neptune, Uranus), composed mostly of gases instead of rock. Also called a Jovian planet. geocorona fuzzy blue layer of hydrogen surrounding the Earth at the upper boundary of the exosphere. gigantic enormous storm in Jupiter's Southern Hemisphere, which has been observed for more than 100 years. greenhouse effect Noun phenomenon where gases allow sunlight to enter Earth's atmosphere but make it difficult for heat to escape. greenhouse gas Noun gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.

Guglielmo Marconi (1874-1937) Italian electrical engineer and inventor. helicopter aircraft that flies using rotating blades on top of the body of the craft. helium a light, colorless gas with the chemical symbol He. hot air balloon bag filled with lighter-than-air gas able to float in the atmosphere. Hubble Space Telescope (1990-present) large, versatile NASA telescope orbiting the Earth. hydrogen Noun chemical element with the symbol H, whose most common isotope consists of a single electron and a single proton. hydrogen sulfide chemical compound gas responsible for the foul odor of rotten eggs. ice satellite in low-Earth orbit that houses several astronauts for months at a time. interplanetary space Noun space within the solar system but outside the atmospheres of any planets or moons. Also called the interplanetary medium. ion Noun electrically charged atom or group of atoms, formed by the atom having gained or lost an electron. ionosphere outer layer of the Earth's atmosphere, 80-400 kilometers (50-250 miles) above the surface.

jet stream between 160 kilometers (100 miles) and 2,000 kilometers (1,240 miles) above Earth's surface. low-pressure system Noun weather pattern characterized by low air pressure, usually as a result of warming. Low-pressure systems are often associated with storms. maneuver mass Noun unit of measurement (abbreviated m) determined by an object's resistance to change in the speed or direction of motion. medium-Earth orbit between 2,000 kilometers (1,243 miles) and 36,000 kilometers (22,370 miles) above the Earths surface. mesopause fluctuating area of the upper atmosphere between the mesosphere and the thermosphere. mesosphere Noun region in Earth's atmosphere between the stratosphere and the thermosphere, about 50-80 kilometers (31-50 miles) above the Earth's surface. meteor Noun person who studies patterns and changes in Earth's atmosphere. methane chemical compound that is the basic ingredient of natural gas. minute smallest physical unit of a substance, consisting of two or more atoms linked together.

mollusk Mount Everest Noun highest spot on Earth, 8,850 meters (29,035 feet). Mount Everest is part of the Himalaya range, in Nepal and China. nacreous pearly, or resembling the inside of a shell. neon chemical element (gas) with the symbol Ne. nitrogen chemical element with the symbol N, whose gas form is 78% of the Earth's atmosphere. noctilucent glowing, high-altitude clouds visible in the twilight sky. ocean path of one object around a more massive object. outer space chemical element with the symbol O, whose gas form is 21% of the Earth's atmosphere. ozone form of oxygen that absorbs ultraviolet radiation. ozone depletion process of the Earth's atmosphere losing ozone. ozone layer Noun (singular: phenomenon) any observable occurrence or feature. photosynthesis Noun process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars. pilot person who steers a ship or aircraft. planet organism that produces its own food through photosynthesis and whose cells have walls. pole extreme north or south point of the Earth's axis.

primitive radio wave Noun electromagnetic wave with a wavelength between 1 millimeter and 30,000 meters, or a frequency between 10 kilohertz and 300,000 megahertz. region Noun any area on Earth with one or more common characteristics. Regions are the basic units of geography. device that moves through the atmosphere by release of expanding gas. sand small, loose grains of disintegrated rocks. satellite imagery photographs of a planet taken by or from a satellite. season rocky debris from space that enters Earth's atmosphere. Also called a meteor. significant solar flare Noun explosion in the sun's atmosphere, which releases a burst of energy and charged particles into the solar system. solar storm Noun sudden change in the Earth's magnetosphere, caused by the solar wind interacting with the Earth's magnetic field. Also called a geomagnetic storm. solar system the sun and the planets, asteroids, comets, and other bodies that orbit around it. solar wind Noun flow of charged particles, mainly protons and electrons, from the sun to the edge of the solar system.

sounding rocket Noun instrument that is launched but does not go into orbit, taking measurements, gathering data, and performing scientific experiments before falling back to Earth. southern lights Noun the bright bands of color around the South Pole caused by the solar wind and the Earth's magnetic field. Also known as the aurora australis. spacecraft vehicle designed for travel outside Earth's atmosphere. specific electrical discharge in the upper atmosphere, usually above thunderhead clouds. storm severe weather indicating a disturbed state of the atmosphere resulting from uplifted air. stratopause fluctuating area of the upper atmosphere between the stratosphere and the mesosphere. stratosphere Noun level of Earth's atmosphere, extending from 10 kilometers (6 miles) to 50 kilometers (31 miles) above the surface of the Earth. sub-orbital flight that has not reached the altitude or velocity to achieve orbit. sulfuric acid toxic chemical made of hydrogen, sulfur, and oxygen. temperature one of the four planets closest to the sun: Mercury, Venus, Earth, or Mars.

thermosphere Noun layer of the Earth's atmosphere located between 80 kilometers (50 miles) and 550 kilometers (341 miles) above the Earth's surface. thunderhead low-level cloud that produces rain, thunder, and lightning. Also called cumulonimbus. Titan largest moon of the planet Saturn. tropopause boundary between the troposphere and the stratosphere layers in the Earth's atmosphere. troposphere Noun lowest layer of the Earth's atmosphere, extending from the surface to about 16 kilometers (10 miles) above. turbopause fluctuating area of the upper atmosphere between the thermosphere and the exosphere. turbulence irregular, violent motion in the atmosphere. ultraviolet radiation Noun powerful light waves that are too short for humans to see, but can penetrate Earth's atmosphere. Ultraviolet is often shortened to UV. universe all known matter, energy, and space. unmanned lacking the physical presence of a person. valley depression in the Earth between hills. vapor visible liquid suspended in the air, such as fog.

volcano Noun an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions. weather balloon Noun hydrogen-filled balloon equipped with tools to measure temperature, humidity, pressure, and other aspects of the atmosphere. weather pattern repeating or predictable changes in the Earth's atmosphere, such as winds, precipitation, and temperatures. weather satellite instrument that orbits the Earth to track weather and patterns in the atmosphere. weather system movement of warm or cold air. wind Noun movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun. X-ray radiation in the electromagnetic spectrum with a very short wavelength and very high energy. zone NWS JetStream - Layers of the Atmosphere Layers of the Atmosphere The envelope of gas surrounding the Earth changes from the ground up. Five distinct layers have been identified using... thermal characteristics (temperature changes), movement, and density. Each of the layers are bounded by "pauses" where the maximum changes in thermal characteristics, chemical composition, movement, and density occur. Troposphere The troposphere begins at the Earth's surface and extends up to 4-12 miles (6-20 km ) high.

This is where we live. As the density of the gases in this layer decrease with height, the air becomes thinner. Therefore, the temperature in the troposphere also decreases with height. As you climb higher, the temperature drops from about 62 °F (17 °C ) to -60°F (-51°C). Almost all weather occurs in this region. The height of the troposphere varies from the equator to the poles. At the equator it is around 11-12 miles (18-20 km) high, at 50 °N and 50 °S , 5½ miles and at the poles just under four miles high. The transition boundary between the troposphere and the layer above is called the tropopause. Together the tropopause and the troposphere are known as the lower atmosphere. Stratosphere The Stratosphere extends from the tropopause up to 31 miles above the Earth's surface. This layer holds 19 percent of the atmosphere's gases but very little water vapor. Temperature increases with height as radiation is increasingly absorbed by oxygen molecules leading to the formation of Ozone.

The temperature rises from an average -76°F (-60°C) at tropopause to a maximum of about 5°F (-15°C) at the stratopause due to this absorption of ultraviolet radiation. This increase is temperature with height means no "convection" occurs since there is no vertical movement of the gases. The transition boundary which separates the stratosphere from the mesosphere is called the stratopause. The regions of the stratosphere and the mesosphere, along with the stratopause and mesopause, are called the middle atmosphere by scientists. Mesosphere The mesosphere extends from the stratopause to about 53 miles (85 km) above the earth. The gases, including the oxygen molecules, continue to become thinner and thinner with height. As such, the effect of the warming by ultraviolet radiation also becomes less and less leading to a decrease in temperature with height. On average, temperature decreases from about 5°F (-15°C) to as low as -184°F (-120°C) at the mesopause. However, the gases in the mesosphere are still thick enough to slow down meteorites hurtling into the atmosphere, where they burn up, leaving fiery trails in the night sky.

Earth's Atmosphere: Composition, Climate & Weather Earth's Atmosphere: Composition, Climate & Weather By Tim Sharp, Reference Editor | September 19, 2012 06:52pm ET MORE Earth is the only planet in the solar system with an atmosphere that can sustain life. The blanket of gases not only contains the air that we breathe but also protects us from the blasts of heat and radiation emanating from the sun. It warms the planet by day and cools it at night. Astronauts aboard the International Space Station took this image showing Earth's atmosphere and moon on July 31, 2011. Credit: ISS Crew Earth Observations Experiment and Image Science & Analysis Laboratory/Johnson Space Center. Earth's atmosphere is about 300 miles (480 kilometers) thick, but most of it is within 10 miles (16 km) the surface. Air pressure decreases with altitude. At sea level, air pressure is about 14.7 pounds per square inch (1 kilogram per square centimeter). At 10,000 feet (3 km), the air pressure is 10 pounds per square inch (0.7 kg per square cm).

There is also less oxygen to breathe. Composition of air The gases in Earth's atmosphere include: Nitrogen – 78 percent Water vapor and other gases exist in small amounts as well. Atmosphere layers Earth's atmosphere is divided into five main layers, the exosphere, the thermosphere, the mesosphere, the stratosphere and the troposphere. The atmosphere thins out in each higher layer until the gases dissipate in space. There is no distinct boundary between the atmosphere and space, but an imaginary line about 68 miles (110 kilometers) from the surface, called the Karman line, is usually where scientists say atmosphere meets outer space. The troposphere is the layer closest to Earth's surface. It is 4 to 12 miles (7 to 20 km) thick and contains half of Earth's atmosphere. Air is warmer near the ground and gets colder higher up. Nearly all of the water vapor and dust in the atmosphere are in this layer and that is why clouds are found here. The stratosphere is the second layer. It starts above the troposphere and ends about 31 miles (50 km) above ground.

Ozone is abundant here and it heats the atmosphere while also absorbing harmful radiation from the sun. The air here is very dry, and it is about a thousand times thinner here than it is at sea level. Because of that, this is where jet aircraft and weather balloons fly. The mesosphere starts at 31 miles (50 km) and extends to 53 miles (85 km) high. The top of the mesosphere, called the mesopause, is the coldest part of Earth's atmosphere with temperatures averaging about minus 130 degrees F (minus 90 C). This layer is hard to study. Jets and balloons don't go high enough, and satellites and space shuttles orbit too high. Scientists do know that meteors burn up in this layer. The thermosphere extends from about 56 miles (90 km) to between 310 and 620 miles (500 and 1,000 km). Temperatures can get up to 2,700 degrees F (1,500 C) at this altitude.

The thermosphere is considered part of Earth's atmosphere, but air density is so low that most of this layer is what is normally thought of as outer space. In fact, this is where the space shuttles flew and where the International Space Station orbits Earth. This is also the layer where the auroras occur. Charged particles from space collide with atoms and molecules in the thermosphere, exciting them into higher states of energy. The atoms shed this excess energy by emitting photons of light, which we see as the colorful Aurora Borealis and Aurora Australis . The exosphere, the highest layer, is extremely thin and is where the atmosphere merges into outer space. It is composed of very widely dispersed particles of hydrogen and helium. Climate and weather Earth is able to support a wide variety of living beings because of its diverse regional climates, which range from extreme cold at the poles to tropical heat at the Equator. Regional climate is often described as the average weather in a place over more than 30 years. A region's climate is often described, for example, as sunny, windy, dry, or humid.

These can also describe the weather in a certain place, but while the weather can change in just a few hours, climate changes over a longer span of time. Earth's global climate is an average of regional climates. The global climate has cooled and warmed throughout history. Today, we are seeing unusually rapid warming. The scientific consensus is that greenhouse gases, which are increasing because of human activities, are trapping heat in the atmosphere. — Tim Sharp, Reference Editor What layer of the atmosphere do we live in? | Reference.com What layer of the atmosphere do we live in? A: Quick Answer Humans live in the layer of the atmosphere referred to as the troposphere. Most of the mass of the atmosphere can be found in the troposphere. Full Answer There are five layers to the Earth's atmosphere. The troposphere is the first layer above the surface and is where the weather of the Earth occurs. The troposphere is heated from below as sunlight warms the ground or ocean, which in turn then radiates the heat into the air. This warm air tends to rise, keeping the air in the troposphere turbulent. The top of the troposphere is very cold. The average temperature there is around -64 degrees Fahrenheit.

The Troposphere - Windows to the Universe Tropospheric Ozone, The Polluter content and activities from Project LEARN The Troposphere The troposphere is the lowest layer of Earth's atmosphere . The troposphere starts at Earth's surface and goes up to a height of 7 to 20 km (4 to 12 miles, or 23,000 to 65,000 feet) above sea level. Most of the mass (about 75-80%) of the atmosphere is in the troposphere. Almost all weather occurs within this layer. Air is warmest at the bottom of the troposphere near ground level. Higher up it gets colder . Air pressure and the density of the air are also less at high altitudes. The layer above the troposphere is called the stratosphere . Nearly all of the water vapor and dust particles in the atmosphere are in the troposphere. That is why most clouds are found in this lowest layer , too. The bottom of the troposphere, right next to the surface of Earth, is called the " boundary layer ". In places where Earth's surface is "bumpy" (mountains, forests) winds in the boundary layer are all jumbled up.

In smooth places (over water or ice) the winds are smoother. The winds above the boundary layer aren't affected by the surface much. The troposphere is heated from below. Sunlight warms the ground or ocean, which in turn radiates the heat into the air right above it. This warm air tends to rise. That keeps the air in the troposphere "stirred up". The top of the troposphere is quite cold. The temperature there is around -55ï¿½ C (-64ï¿½ F)! Air also gets 'thinner' as you go higher up . That's why mountain climbers sometimes need bottled oxygen to breathe. The boundary between the top of the troposphere and the stratosphere (the layer above it) is called the tropopause. The height of the tropopause depends on latitude, season, and whether it is day or night. Near the equator, the tropopause is about 20 km (12 miles or 65,000 feet) above sea level. In winter near the poles the tropopause is much lower. It is about 7 km (4 miles or 23,000 feet) high. The jet stream is just below the tropopause.

This "river of air" zooms along at 400 km/hr (250 mph)! Last modified January 11, 2010 by Randy Russell . Shop Windows to the Universe Science Store! Cool It! is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate changeï¿½and how policy and technology decisions made today will matter. Cool It! is available in our online store . Windows to the Universe Community News

Question: The lowest part of the Earth's atmosphere, where we live, is called what?
Answer: The Troposphere